1) Field of the Invention
The present invention relates to a device for adjusting the prestress of an elastic means, especially the prestress of a spring used to adjust height of and the relief force acting on a weight, especially on the weight of a patient within a locomotion training means to be used for walking therapy of paraparetic or hemiparetic patients. In other words, the invention relates generally to an automatic adjusting device for the prestress deviation of a spring in an operating point and especially to an automatic unloading device that allows unloading an object attached to one end of a rope by a precise counter force. Especially, the invention relates to a device and a process which can be used within a locomotion training of patients with walking impairments in any phase of rehabilitation.
2) Description of Related Art
As mentioned above said type of unloading system can be used for different applications but is preferably intended for the use in body weight supported treadmill training. This type of training is for example being used to train neurologically impaired patients to walk again during rehabilitation. For such incomplete paraplegic patients the possibility exists of improving walking ability up to normality by means of adequate locomotion training. The required therapy at present takes place on a treadmill, where walking is first made possible for the patient by defined weight relief and partially by additional assisting guidance of the legs by physiotherapists (Wickelgren, I. Teaching the spinal cord to walk. Science, 1998, 279, 319-321).
In the rehabilitation of patients with limited motion of the legs or after orthopedic operations, various driven orthoses are already in use which actively move the legs of recumbent patients. During body weight supported treadmill training, a patient is walking on a treadmill, while he is partially suspended from part of his body weight.
EP 1 137 378 discloses an automatic machine which is used in treadmill therapy (walking therapy) of paraparetic and hemiparetic patients and which automatically guides the legs on the treadmill. Said machine consists of a driven and controlled orthotic device which guides the legs in a physiological pattern of movement, a treadmill and a relief mechanism. The knee and hip joints of the orthotic device are each provided with a drive. Said orthotic device is stabilized on a treadmill with stabilizing means in such a manner that the patient does not have to keep his/her equilibrium. The orthotic device can be adjusted in height and can be adapted to different patients.
The unloading is achieved by a counterweight that is attached to the other end of a rope, which is connected to the patient by a harness. This is by definition a simple method and the results are often acceptable for regular treadmill training. However, there are some disadvantages in using this method for this kind of therapy. One disadvantage is occurring if the patient has to be suspended by a large amount of his body weight. If a large mass has to be attached on the other side of the rope the inertia of the mass is causing large forces during the up and down acceleration of the body. Also, it is not very easy to change the amount of unloading during the training with most of the conventional counterweight systems. Either the therapist has to lift weight to or from the system to change the suspension or the patient has to be lifted by a winch to be able to connect additional counterweights to the system.
U.S. Pat. No. 5,273,502 discloses a device using two different cable length adjustment means to provide a reliable positioning of the device height. Another limitation of this approach is furthermore the limited liberty of changes to be made in the course of the application of the walking program for the patient.
The not prepublished EP 1 586 291 from the applicant shows a solution for the adjustment problem through use of an electronic control device. However, it is a demand of the market to equip such a device with a less costly control device.
Since the relief force is achieved through use of a spring means, one object of the invention is therefore to describe a simpler device and a process for adjusting the change in prestress around an operating point of a spring.
One further object of the invention is to describe a device allowing quick response times and precise determination of the height of the patient's position and of the relief force through simpler, i.e. less complex, means.
It is an further object of the invention to realize a mechanism wherein an elastic means having a linear or non-linear path-dependent or stroke-dependent force progression nevertheless provides an almost constant force within a given motion range or stroke.
U.S. Pat. No. 5,273,502 discloses a winch as a principal cable length adjustment means. This adjustment means always acts on the same length of cable providing different aging effects on wound and unwound parts of said cable and asks for a strong motor to achieve the necessary counter force for a person to be lifted.
It is a further object of the invention to describe a device allowing better adjustment of the height of a patient's position and improved aging properties of the corresponding cable.